The invention concerns a device for checking the construction of an extruder screw consisting of a shaft and screw elements that are to be pushed or have been pushed one after the other onto said shaft in a defined sequence, each screw element having an element-specific external geometry.
As is known, extruders serve for preparing compounds that are being processed in a working unit or a barrel by way of one or more extruder screws rotating there. Merely by way of example, mention may be made of polymer compounds, which are melted and compounded in the extruder, to be subsequently processed further, for example for the forming of granules of plastic, or in the course of injection-molding work for the production of components and the like. Mention may also be made by way of example of pharmaceutical compounds that serve for the production of medicaments, for example in the form of tablets. Here, too, the corresponding materials are processed and mixed etc. in the barrel by way of the screws, in order to achieve the desired homogeneous composition of the extrudate. In order to make this possible, one or more further devices is/are provided on the working unit or assigned to the working unit, such as for example corresponding feeding devices, by way of which the materials to be processed are charged in a metered manner, or heating devices, which serve for controlling the temperature of the barrel or the barrel sections from which such a barrel is usually composed, and the like. Also in the food sector, corresponding compounds are often prepared using an extruder.
The one or more extruder screws serving directly for the processing of the material is/are essential for the function of the extruder. Depending on the material to be prepared and according to the corresponding working task, a distinction can be made between different types of screw. Known screws are those referred to as compact screws, which are made from one piece. This means that the specific screw geometry is fashioned directly from a single block of material. Other known screws are those referred to as fitted extruder screws, in the case of which a multiplicity of individual screw elements are fitted in series onto a shaft, the screw elements and the screw shaft being connected to one another in a fixed rotational relationship by way of corresponding interlocking tooth arrangements. Each screw element has a certain geometry, which gives the screw element its typical function. Usually 20-30 individual screw elements, if need be even more, are fitted onto a shaft, so that in the end a relatively complex overall geometry is obtained. Each individual extruder screw produced in this way is thereby designed very specifically with regard to its geometry for a certain working process, which means that a certain screw is assigned to a certain working task, which in turn is assigned specific operating parameters, which the operator of the control device must set for operating the extruder. This means that the sequence in which the individual screw elements are pushed onto the shaft must be precisely maintained in order to avoid fitting errors, which would result in a changed geometry that is unsuitable for the intended working process. Since each individual screw element is allocated a certain function, for example a conveying function or a kneading function or a mixing function and the like, in each case resulting from the element-specific external geometry, each fitting error consequently has the effect that—if the wrongly fitted screw shaft can be installed at all—the desired working result is not achieved.
Even if the operator applies a high degree of precision and care when fitting together or constructing the extruder screw, fitting errors can nevertheless not be ruled out entirely, since it is a purely manual activity that is concerned.